Air bag start control device of vehicle

ABSTRACT

An air bag start control device of vehicle capable of optimally controlling the operation of an air bag by determining whether a person is seated on a vehicle seat or not and, when seated, by determining the body form thereof, wherein an air bladder type pressure sensor is fitted to either or both of the back rest and seat part of the vehicle seat to control the amount and the direction of inflation of the air bag according to whether or not living body signals such as respiration and pulsation are included in electric outputs from the pressure sensors, when included, according to whether the outputs exceed specified limits or not.

TECHNICAL FIELD

This invention relates to a vehicular airbag control system forcontrolling such performance parameters of an airbag as triggering ornon-triggering thereof, and the force and direction of airbag inflation,using a pneumatic pressure sensor or sensors installed in a vehicle seatfor determination of the specifics of the particular occupant of theseat.

BACKGROUND ART

Airbags have found widespread use on motor vehicles for safe-guardingthe drivers and passengers against traffic accidents by mitigating theimpacts of collision. Mounted in front of or on the sides of the vehicleseats, airbags are sealed hermetically and each furnished with aninflation device including a solid propellant. The propellant isdetonated in the event of an abrupt change in vehicle acceleration dueto a collision. The gas created by the detonated propellant instantlyinflates the bag thereby causing the same to keep the occupant of theseat confined thereto against the momentum of the collision.

As heretofore constructed, however, a great majority of airbags have hadtheir performance predetermined in terms of bag volume upon inflation,the angle of deployment and so forth in consideration of average sizeadults. Little or no attention has been paid in most cases to thespecific figures and weights of the individual seat occupants. Theairbags of such average design could inflict excessive impact uponinfants and small children when deployed, sometimes hurting them nearlyas seriously as the collision itself.

An additional inconvenience heretofore encountered with the airbags isthat they could be triggered off even when the seats were unoccupied orwhen luggage was placed thereon. Inflated unnecessarily, the airbagscould send such luggage hurtling off the seats. Both driver andpassengers might also suffer from a sudden pressure change caused insidethe vehicle by the unnecessarily inflated airbags. The airbags shouldtherefore be prevented from deployment when the associated seats areunoccupied or merely occupied by luggage.

DISCLOSURE OF THE INVENTION

The present invention provides an airbag control system having apneumatic pressure sensor or sensors mounted to each vehicle seat inorder to ascertain whether the seat is occupied or not. Luggage isdiscriminated from humans if the sensor output signal or signals have nosustained periodicity indicative of such rhythmic bodily processes aspulsation and respiration, which are distinguishable from the bumps andjolts of the vehicle. If the sensor output signal or signals representthe rhythmic bodily processes, on the other hand, then the body size ofthe seat occupant is determined on the basis of the signal magnitude.

All the foregoing considerations lead to optimal control of the airbagsdepending upon the body size of the seat occupants and other factors.Optionally, the airbag control system according to the invention may bemade active only during vehicle travel as ascertained from informationcontained in the sensor output signals above or from some other sourceon the vehicle.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle seat fitted with pneumaticpressure sensors used in the airbag control system according to theinvention.

FIG. 2 is an enlarged perspective view of each pressure sensor of FIG.1.

FIG. 3 is a graph plotting the curve of the pressure sensor output whena human sits on the vehicle seat, the sensor output here beingindicative of human respiration.

FIG. 4 is a graph of the output from the pressure sensor on the seatback when an adult of average body size is seated motionlessly while thevehicle is at a standstill, the seat-back pressure sensor output beingshown after being processed by a waveform analyzer.

FIG. 5 is a graph of the output from the pressure sensor on the seatbottom when the vehicle is traveling with the seat unoccupied, theseat-bottom pressure sensor output being shown after being processed bya waveform analyzer.

FIG. 6 is a graph of the output from the seat-bottom pressure sensorwhen the vehicle is traveling with the seat loaded with luggage, theseat-bottom pressure sensor output being shown after being processed bya waveform analyzer.

FIG. 7 is a graph of the output from the seat-bottom pressure sensorwhen the vehicle is traveling with the seat occupied by a human, theseat-bottom pressure sensor output being shown after being processed bya waveform analyzer.

FIG. 8 is a block diagram of the airbag control system according to theinvention for optimizing the performance of the airbag by detecting thehuman or luggage on the seat from the seat-back and seat-bottom pressuresensor outputs.

FIG. 9 is an illustration of how the airbag is inflated under thedirection of the airbag control system.

BEST MODE OF CARRYING OUT THE INVENTION

The present invention will now be described in terms of the illustratedembodiment thereof. The pneumatic pressure sensors for use in thepractice of the invention may each be constructed as depicted in FIG. 2and therein generally designated 2. The pressure sensor 2 includes apneumatic sensing bag 21 of relatively thin, elongate boxlike shapefabricated from rubber or like pliant plastics. The sensing bag 21 neednot be perfectly airtight; rather, for ease of mass production andimmunity from ambient temperature changes, it may have pinholes,permitting some slight inflow and outflow of air. The sensing bag 21should not, however, be allowed to get flattened out but should retainits original shape as long as possible, as by being stuffed with spongeor the like.

Communicatively joined to one end of the sensing bag 21 is a conduit 22leading to a microphone 23. Pressure variations created inside thesensing bag 21 are therefore conveyed via the conduit 22 to thediaphragm of the microphone 23. The electric output from the microphone23 is sent over conductors 24 to an electric circuit 25 thereby to beprocessed as required preparatory to transmission, either by radio orover wires.

The microphone 23, conductors 24 and electric circuit 25 may all becombined into one-piece construction by being accommodated in a singlehousing. It is also possible to install the microphone 23 inside thesensing. bag 21, thereby forgoing the conduit 22.

FIG. 3 graphically indicates the amplitude of the respiration signalproduced by the electric circuit 25 when a human sits on the vehicleseat in various positions with respect to the pressure sensor 2. Thevertical axis of the graph represents the amplitude in millivolts (mV)of the respiration signal generated by the pressure sensor 2, whereasthe horizontal axis represents the percentage of seat occupantdisplacement with respect to the sensing bag of the pressure sensor. Theoccupant displacement percentage is calculated by first subtracting thearea of that part of the sensing bag surface which is actually occupiedby the driver or passenger, from the total area of the sensing bagsurface, then by dividing the difference by the total area of thesensing bag surface, and then by multiplying the result of the divisionby 100.

A closer study of the graph will now prove that the pressure sensoroutput magnitude is substantially constant when the occupantdisplacement percentage is up to 30, abruptly drops above that value,and becomes zero when the percentage rises to 70. This sudden drop insignal strength may be explained as follows:

When the occupant displacement percentage becomes so high that only onehalf or so of the sensing bag is weighed down by the seat occupant, theother, unloaded part of the sensing bag starts absorbing verysubstantive part of the internal pressure variations caused by therespiration or other bodily motion of the occupant. Thus, it isreasoned, the sensing bag fails to convey a corresponding proportion ofits internal pressure changes to the microphone 23. The presentinvention takes positive advantage of this sensing loss of the sensingbag on the vehicle seat for controlling the performance of theassociated airbag or airbags.

As illustrated in FIG. 1, each vehicle seat may be furnished with twopneumatic pressure sensors each constructed as set forth above withreference to FIG. 2. The vehicle seat 1 has the sensing bag 21A of onepressure sensor mounted centrally and internally of its back 11. Thissensing bag 21A should be sufficiently large to cover most of the backof the seated adult, typically about 50 centimeters in verticaldimension and about 30 centimeters in horizontal dimension. Theseat-back pressure sensor additionally comprises the conduit 22A,microphone 23A, conductors 24A and electric circuit 25A. The electriccircuit 25A sends the seat-back sensor signal A by radio or over wires.

Another pressure sensor has its sensing bag 21B mounted centrally andinternally of the bottom 12 of the vehicle seat 1. The sensing bag 21Bof this seat-bottom pressure sensor should be large enough to cover thethighs of an adult, typically about 40 centimeters in vehicleside-to-side transverse dimension and about 25 centimeters in vehiclefront-to-rear depth dimension. The seat-bottom pressure sensoradditionally comprises the conduit 22B, microphone 23B, conductors 24Band electric circuit 25B. The electric circuit 25B transmits theseat-bottom sensor signal B by radio or over wires.

The outputs A and B from both seat-back pressure sensor and seat-bottompressure sensor are at zero level when the vehicle is standing stilland, at the same time, when the seat is empty or has luggage placedthereon.

FIG. 4 graphically represents the result of waveform analysis of theseat-back pressure sensor output A when the vehicle is standing stilland, at the same time, when an average-size adult sits motionlessly onthe seat. The vertical axis of the graph represents the sensor outputmagnitude in volts, and the horizontal axis represents time in seconds.It will be noted from this graph that the seat-back pressure sensoroutput contains a nearly sinusoidal waveform, with a cycle ofapproximately four seconds, indicative of the bodily motion of the seatoccupant due to respiration. Superposed on this sinusoidal waveform aresmaller undulations due to less pronounced physical movements such aspulsation, which manifest themselves even when the human is seatedstill.

The output B from the seat-bottom pressure sensor under like conditionsis analogous in waveform with the seat-back pressure sensor output A.There does, however, exist a difference in signal magnitude by reason ofthe difference in cushioning between seat back 11 and seat bottom 12.

FIG. 5 is a graphic representation of the waveform-analyzed seat-bottompressure sensor output B when the vehicle is running with the seatunoccupied. Theoretically, the seat-bottom pressure sensor output levelshould be zero under the noted conditions, but, actually, minutefluctuations are observable in signal level. Such fluctuations areascribable to the fluttering of the sensing bag 21B due to vehiclevibration, and to the consequent pressure variations inside the bagwhich are sensible by the microphone. Whatever the reason may be, theseminute fluctuations in sensor output level bear no significance and arenegligible.

Graphically represented in FIG. 6 is the waveform-analyzed seat-bottompressure sensor output B when the vehicle is running with luggage placedon the seat, or more exactly, on the sensing bag 21B of the seat-bottompressure sensor. The luggage used in this experiment was boxlike inshape, sized 30 by 30 by 30 centimeters and weighing approximately fivekilograms.

The seat-bottom pressure sensor output B contains pulses because ofchanges in the force of gravity due to vehicle vibration, particularlyin the vertical direction. All such pulses are of brief durations. Themean level of the seat-bottom pressure sensor output B is zero.

The seat-back pressure sensor output A will be approximately zero inlevel, as is the seat-back pressure sensor output B of FIG. 6, if theluggage on the seat is out of contact with the sensing bag 21A of theseat back pressure sensor or in contact with less than 30 percent of thesurface area of the sensing bag 21A. On the other hand, if the luggageis in contact with more than 30 percent, especially more than 50percent, of the surface area of the seat-back sensing bag 21A, theseat-back pressure sensor output A will be more or less similar inwaveform to the seat-back pressure sensor output B of FIG. 6.

FIG. 7 is a graphic representation of the waveform-analyzed seat-bottompressure sensor output B when the vehicle is running with the seatoccupied by a human. The output B contains pulses of considerableamplitude and repetition rate due both to vehicle variations,particularly vertical, and to the cushioning effect peculiar to thehuman body. It will nevertheless be observed that the output B as awhole has a sinusoidal waveform representative of human respiration. Notonly respiration but also heartbeat is detectable from this sensoroutput by a discriminator yet to be described.

The following tabulated judgments are derivable from the variouscombinations of the seat-back pressure sensor output A and seat-bottompressure sensor output B of different magnitudes, including zero. Whenthe vehicle is at rest, the judgments are made as in Table 1 on thebases of the magnitudes of the bodily process signal components, such asthose representative of human respiration and heartbeat, of the pressuresensor out-puts A and B. Different reference values are set for thesensor outputs A and B because of the different cushioning capabilitiesof the seat back and seat bottom. TABLE 1 Seat-Back Sensor Seat-BottomSensor Output A Output B Judgments more than reference Q more thanreference S adult of average body size or more more than reference Qless than reference S slim less than reference Q more than reference Sfat less than reference Q less than reference S child more thanreference R more than reference T less than reference R less thanreference T child seat occupied more than zero more than zero zero zeroluggage or unoccupied

When the vehicle is traveling, on the other hand, judgments are made asin Table 2 below on the bases of not only human respiration, heartbeatand like bodily process components of the sensor outputs A and B butalso the signal components representative of vehicle vibration. Thevibration of the traveling vehicle provides random noise, which remainssuperposed on the sensor outputs A and B even after they have passedthrough a respiration and heartbeat filter included in the airbagcontrol system. The reference values during vehicle travel musttherefore differ from those during vehicle rest. TABLE 2 Seat-BackSensor Seat-Bottom Sensor Output A Output B Judgments more thanreference U more than reference X adult of average body size or moremore than reference U less than reference X slim less than reference Umore than reference X fat les than reference U less than reference Xchild more than reference V more than reference Y less than reference Vless than reference Y child seat occupied more than reference W morethan reference Z less than reference W less than reference Z luggage(child seat unoccupied) approx. zero approx. zero unoccupied

The particular reference values for the foregoing judgments must bedetermined in each application of the invention depending upon suchvariables as vehicle seat configurations and the shape and material ofthe sensing bags in use. Normally, the reference values may be selectedin the 35-65 range of seat occupant displacement percentage in the graphof FIG. 3, where the sensor output amplitude varies steeply.

Block-diagrammatically illustrated in FIG. 8 is a preferred form ofairbag control system according to the invention whereby airbagperformance is controlled for optimal results depending upon theparticular human or nonhuman occupant, if any, of the seat asascertained from the sensor outputs A and B. The microphones of the twopressure sensors provide these sensor outputs at 81A and 81B in FIG. 8.The seat-back pressure sensor output A is directed through an amplifier82A into a bandpass filter 83A. This bandpass filter may have a passbandof from about 0.1 Hz to about 1.0 Hz for detection of respiration, andof from about 3 Hz to about 15 Hz for heartbeat detection.

Issuing from the bandpass filter 83A, the seat-back sensor outputcontaining the desired bodily process signal component is fed into alevel detector 84A. This level detector puts out a pulse each time theinput signal rises to a predetermined level. A counter 85A counts thepulses from the level detector 84A, putting out a pulse for every twoincoming pulses. A timer 86A is turned on by each output pulse of thelevel detector 84A and off by each output pulse of the counter 85A, inorder to measure the duration of each period of the periodic signal.

Besides being directed into the level detector 84A as above, the outputfrom the bandpass filter 83A, possibly representative of the seatoccupant's respiration and heartbeat, is integrated or has its peakdetected at 87A. The output from this circuit 87A is directed into thearithmetic unit 88 of a central processor unit (CPU) for comparison withthe predetermined reference values.

Similarly, the seat-bottom pressure sensor output B is sequentiallydirected into and through an amplifier 82B, bandpass filter 83B, leveldetector 84B, counter 85B, timer 86B, and arithmetic unit 88. The outputfrom the bandpass filter 83B is also fed into an integrator or peakdetector 87B and thence into the arithmetic section 88. The arithmeticunit 88 compares the input signals from the reference values and makesthe necessary judgments as in Tables 1 and 2. These judgments areutilized by an airbag controller 89 in order to generate signals forcontrolling the airbag accordingly.

FIG. 8 further indicates at 90 a vehicle travel signal generator whichputs out a signal indicative of whether the vehicle is traveling or not.The vehicle travel signal generator 90 may sense vehicle travel eithermechanically or electrically, as from the rotation of some rotary partof the vehicle. Alternatively, the pressure sensor output A or B may befiltered to derive a signal component indicative of vehicle travel.

The output from the vehicle travel signal generator 90 is directedthrough a level detector 91 into the arithmetic unit 88. Judging fromthe input signal whether the vehicle is running or not, the arithmeticunit 88 switches the reference values for comparison. It is alsopossible to confine the airbag to one prescribed mode of operationdepending upon whether the vehicle is running or at a standstill.

FIG. 9 is explanatory of how the airbag operates under the direction ofthe airbag controller 89. At 1 is shown the vehicle seat in side view,in front of which there is the dashboard having a cover 91 whichnormally closes the airbag compartment of the dashboard. The airbagcompartment cover 91 is shown open, with the airbag indicated by thesolid line as inflated to the full, that is, to the conventionallystandard size.

Let it be assumed that a collision has occurred while the pressuresensor outputs A and B are greater than the reference values U and X,respectively. The airbag controller 89 will then cause the airbagactivator, not shown, to deploy the airbag normally, that is, fully, asindicated by the solid-line outline designated 92 in FIG. 9.

If then the sensor outputs A and B are such that the arithmetic unit 88determines that a child is seated, the airbag controller 89 will thencause the airbag to be inflated to an extent, and in a direction,fitting the child. The airbag inflated in this manner is delineated bythe dot-and-dash outline 92A in FIG. 9. For a seat occupant with a bodysize in between, the airbag may be inflated as depicted by the dashedoutline 92B.

In order to control the extent to which the airbag is inflated as above,the airbag propellant may be prepared in several separate dosages, anddifferent numbers of such propellant dosages may be detonated. Thedirection of airbag deployment is controllable by the angle throughwhich the airbag compartment cover 91 is opened.

INDUSTRIAL APPICABILITY

Thus the present invention makes it possible to determine whether thevehicle seat is occupied or not, whether the occupant is a human orluggage, and, if it is a human, what is his or her body size. The airbagis triggered or not triggered depending upon these findings, and when itis, inflated to an optimal extent and in an optimal direction for theparticular seat occupant, thereby guarding the occupant from thecollision without inflicting secondary damage. The invention istherefore of particular utility as a safety device of motor vehicles,particularly passenger cars.

1. A vehicular airbag control system for controlling an airbag mountedadjacent a vehicle seat, comprising: (a) a pneumatic pressure sensormounted to a back of a vehicle seat for providing a bodily processsignal indicative of such bodily processes as respiration and pulsation;(b) means for comparing the magnitude of the bodily process signal witha predefined reference value; and (c) means for controlling the extentand direction of airbag inflation according to the results of comparisonof the bodily process signal with the reference value.
 2. A vehicularairbag control system for controlling an airbag mounted adjacent avehicle seat, comprising: (a) a pneumatic pressure sensor mounted to abottom of a vehicle seat for providing a bodily process signalindicative of such bodily processes as respiration and pulsation; (b)means for comparing the magnitude of the bodily process signal with apredefined reference value; and (c) means for controlling the extent anddirection of airbag inflation according to the results of comparison ofthe bodily process signal with the reference value.
 3. A vehicularairbag control system for controlling an airbag mounted adjacent avehicle seat, comprising: (a) a first pneumatic pressure sensor mountedto a back of a vehicle seat for providing a first bodily process signalindicative of such bodily processes as respiration and pulsation; (b) asecond pneumatic pressure sensor mounted to a bottom of a vehicle seatfor providing a second bodily process signal indicative of such bodilyprocesses as respiration and pulsation; (c) means for comparing themagnitudes of the first and the second bodily process signal with afirst and a predefined reference value, respectively; and (d) means forcontrolling the extent and direction of airbag inflation according tothe various combinations of the results of comparison of the first andthe second bodily process signal with the first and the second referencevalue.
 4. The airbag control system of claim 3 further comprising meansfor preventing the airbag from being inflated when both first and secondbodily process signals are not contained in outputs from the first andthe second pressure sensor.